The present invention relates generally to a thermal barrier coating system for a component that is exposed to high temperatures, such as a gas turbine engine component (e.g. blades, vanes, etc.). More particularly, the present invention relates to the formation of a thermal barrier coating system.
A gas turbine engine component (“component”), such as a blade tip, blade trailing edge, blade platform, blade airfoil, vane airfoil, vane trailing edge, or vane platform, is typically exposed to a high temperature and high stress environment. The high temperature environment may be especially problematic with a superalloy component. Namely, the high temperatures may cause the superalloy to oxidize, or weaken which then decreases the life of the component. In order to extend the life of the component, a thermal barrier coating system (TBC system) may be applied to the entire superalloy component or selective surfaces, such as surfaces of the superalloy component that are exposed to the high temperatures and other harsh operating conditions. A TBC system protects the underlying material (also generally called the “substrate”) and helps inhibit oxidation, corrosion, erosion, and other environmental damage to the substrate. Desirable properties of a TBC system include low thermal conductivity and strong adherence to the underlying substrate.
The TBC system typically includes a metallic bondcoat or oxidation resistant coating and a ceramic topcoat (i.e., a thermal barrier coating or TBC topcoat). The bondcoat is applied to the substrate and aids the growth of a thermally grown oxide (TGO) layer, which is typically alpha aluminum oxide, (Al2O3 or “alumina”). Specifically, prior to or during deposition of the TBC topcoat on the bondcoat, the exposed surface of the bondcoat can be oxidized to form the alumina TGO layer or scale. The TGO forms a strong bond to both the topcoat and the bondcoat, and as a result, the TGO layer helps the TBC topcoat adhere to the bondcoat. The bond between the TGO and the topcoat is typically stronger than the bond that would form directly between the TBC topcoat and the bondcoat. The TGO also acts as an oxidation resistant layer, or an “oxidation barrier”, to help protect the underlying substrate from damage due to oxidation.
The success of a TBC system depends on certain procedures used during deposition, including surface cleaning operations.